The present invention relates to a process and an apparatus for preparing active ingredient dispersions.
It is nowadays necessary in many sectors of the chemical industry to prepare active ingredient dispersions, eg. in the color and dye industry and the drugs industry. In this connection it is often impossible to disperse. the active ingredient, eg. the dye or the drug, directly in an aqueous liquid. In particular, the active ingredient particles are then not in the desired micronized form.
The preparation of very finely divided, micronized carotenoids in an aqueous dispersion is described in DE-A 29 43 267. In this case, a carotenoid is dissolved in a supercritical gas in an autoclave, and the resulting solution is dispersed in a suitable aqueous colloidal matrix, which is located in a second autoclave, using an agitator. The resulting dispersion consists of droplets of fluid gas containing active ingredient in water. This two-phase system is decompressed, with the gas being continuously discharged from the autoclave, whereas the liquid can be removed only batchwise after completion of the process. This process results in an average particle size of the carotenoid of less than 1 micron. A disadvantage is that phase separation may occur during the decompression process so that the active ingredient is insufficiently stabilized by the liquid matrix. In addition, a loss of active ingredient must be accepted.
European Patent 0 322 687 proposes a process for preparing a drug form comprising an active ingredient and a carrier. This entails a fluid gas, an active ingredient and carrier materials, which can also be dissolved in a liquid, being introduced into a spray tower so that the fluid gas picks up active ingredient and carrier. The fluid gas is subsequently separated from the resulting active ingredient/carrier combination in a separator so that the combination can be removed from the separator. This process produces dry active ingredient particles but not liquid dispersions. Fluid gas means a substance which is in the form of a gas or vapor under atmospheric pressure and which has been compressed to the vicinity of its critical point or beyond and is therefore in the form of a sub- or supercritical fluid.
It is an object of the present invention to provide a process and an apparatus for preparing active ingredient dispersions which lead to a particularly fine dispersion of the active ingredient in the dispersion. In particular, the micronized active ingredients must not agglomerate.
We have found that this object is achieved by the process described herein. This entails an active ingredient being dissolved in a fluid gas, and the fluid gas loaded with active ingredient being finely dispersed in a liquid and, during this, essentially completely dissolved. The solid is formed during the dissolving process of the fluid gas. Each of the individual, finely distributed gas bubbles contains only little solid, so that the solid particles produced therein are very small. Since the particles pass directly into the liquid, where they are preferably bound into protective colloids, and previously only little solid is contained in each of the individual, finely distributed gas bubbles, agglomeration can be virtually ruled out. The solution is then decompressed, and the gas is thus separated from the liquid loaded with active ingredient. Part of the removed liquid loaded with active ingredient is preferably reused as dissolving liquid for the fluid gas. It is possible in this way to achieve a high concentration of the micro-particles in the dispersion, irrespective of the solubility of the active ingredient in the fluid gas. Another preferred process is one in which the solution is not on decompression completely decompressed to atmospheric pressure so that the reused liquid loaded with active ingredient is preloaded with the fluid gas. It is possible in this way to influence both the rate of formation of the solid particles and the morphology thereof. Furthermore, the complete dissolving of the gas in the liquid ensures that the active ingredient passes completely from the gas into the liquid. The process can be carried out continuously or batchwise, and in both cases there is no, or only negligible, agglomeration of particles, preferably because of the stabilization by protective colloids.
The object is also achieved by a process in which an active ingredient is dissolved in a fluid gas, and the fluid gas loaded with active ingredient is dispersed in a liquid saturated with this gas, so that a first dispersion of liquid and fluid gas loaded with active ingredient is formed. The active ingredient is in this case transferred to the phase boundary by molecular diffusion from the gas. The solid then forms only at the phase boundary and passes from there directly into the liquid, where it is immediately stabilized, preferably by protective colloids, so that agglomeration is ruled out. This first dispersion is passed through a holdup section to form a second dispersion of liquid loaded with active ingredient and fluid gas. The second dispersion is then separated, without previous decompression, by phase separation into a gas phase and a third dispersion of liquid and active ingredient. Part of the third dispersion is finally reused to form the first dispersion with the fluid gas. It is advantageous that a large part of the gas can be reused for dissolving the active ingredient without renewed compression.
In another embodiment, an active ingredient is dissolved in a fluid gas, and the fluid gas loaded with active ingredient is decompressed to form a first dispersion of gas and active ingredient. This first dispersion is dispersed in a liquid to give a second dispersion which is passed through a holdup section and separated into a gas phase and a third dispersion of liquid and active ingredient. Preferably part of the third dispersion which has been separated off is reused as liquid to form the second dispersion.
It is preferred to recycle the gas which has been separated off and is reused as fluid gas for dissolving the active ingredient. The active ingredient used preferably consists of a mixture of a plurality of active ingredients. Preferred active ingredients are dyes, vitamins, carotenoids, polymers, liposomes, drugs or crop protection agents. Preferred fluid gases are CO2, N2O, ethylene, propane, H2O, NH3, hydro-carbons, alcohols and mixtures of these substances The preferred liquid used is water or an organic solvent which is preferably supplemented with additions of protective colloids such as surfactants, polymers, celluloses, dextrins or proteins such as gelatin and/or emulsifiers or the like.
The object of the invention is also achieved by the apparatus described herein. An apparatus according to the apparatus claims comprises an extractor for dissolving an active ingredient in a fluid gas, which is connected via a line to a mixer for dissolving the fluid gas loaded with active ingredient in a liquid. The liquid is fed to the mixer through another line. The apparatus additionally contains a holdup section which is connected to a separator in which the gas is separated from the liquid containing active ingredient. The separator has discharge lines for the gas which has been separated off and for the liquid which has been separated off. The apparatus additionally contains a return feed for part of the liquid which has been separated off to the mixer.
A decompression valve is preferably fitted between the holdup section and the separator. In a preferred embodiment, the discharge line for the gas which has been separated off returns the latter from the separator to the extractor.